Kernel-Managed Swap Facility (KMSF) Manual

Introduction
Kernel-Managed Swap Facility (KMSF) Manual—425824-005
1-7
Characteristics of KMS Files
The operating system swaps data to the swap file as needed. If the process attempts
to access a page that it has written to and that the operating system has swapped out,
a page-fault interrupt is generated. The page-fault interrupt handler passes the access
request to the operating system, which works with the disk process to read the absent
page in from disk. The operating system makes the page available to the executing
process, which can then resume execution. Figure 1-3 illustrates how data is read from
swap files.
When the process terminates, the swap space and the reservation are returned to
KMSF, and the facility frees the space for use by another process.
Characteristics of KMS Files
A KMS file:
•
Is opened for exclusive access by the operating system monitor process and is
secured to prevent reading by non-privileged processes
•
Contains data for various processes, and the data from each process can be
distributed over multiple swap files
•
Is used by only one processor, but a single processor can have several dedicated
swap files
Figure 1-3. How Data is Read from Swap Files
Interrupt for
absent page
$SWAP
Page made available
to the process
Read page
request
Absent page
read from disk
Executing
Process
Operating
System
Disk
Process
Page -Fault
Interrupt Handler
swap00
swap01
VST003.vsd